High frequency current generator



Nov. 13, 1962 A. JAKOUBOVITCH HIGH FREQUENCY CURRENT GENERATOR 2 Sheets-Sheet 1 Filed April 4, 1960 Nov. 13, 1962 A. JAKOUBOVITCH HIGH FREQUENCY CURRENT GENERATOR 2 Sheets-Sheet 2 Filed April 4, 1960 FIGS FiGA- lnvemor ALBERT JAKOUBDVITCH Afforneys United States Patent 0 3,064,103 HIGH FREQUENCY CURRENT GENERATOR Albert Jakoubovitch, Paris, France, assignor to Societe de lElectronique Francaise, Asnieres, France, a body corporate of France Filed Apr. 4, 1960, Ser. No. 19,560 Claims priority, application France Apr. 7, 1959 t 8 Claims. *(Cl. 21910.75)

'The present invention concerns a high-frequency current generator, particularly 'for heating by induction or by di-electric loss.

In some known. embodiments of high-frequency generators for industrial use, the energy of the oscillating circuit is taken by means of a transformer, the primary of which forms at least a part of the self-inductance of said circuit, while its secondary is connected to the consuming apparatus.

The high-frequency current generators for the above mentioned use must include means to vary within wide limits, and preferably continuously, the energy transmitted to the consuming apparatus, while the energy pro duced by the oscillating circuit must be kept practically constant, so that the working of the electron tube which maintains the oscillations in said circuit, remains within limits whichensurc optimum output.

In the known generators of this type, this result is generally obtained by using transformers-having a continuously variable coupling between their primary and secondary winding s. a

The transformers used in known generators of this type allow to vary the energy transmitted to the consuming apparatus only within relatively narrow limits, particularly since it is not possible to give to their coupling values about 0 and about 1; on the other hand, the fixedness of the self impedance of their secondary winding limits the possibility of adjusting the generator to its'load: for instance, in induction heating, it is difficult to empirically determine theinduction coil so as to obtain the optimum generator output. v

One object of the invention is to provide a high-frequency current generator which presents none of the inconveniences of the known generators above mentioned.

Another object of the invention is to provide a high frequency current generator including a transformer in which at least one of the turns of the secondary winding is made in two parts, hinged the one to the other so that they can be displaced by pivoting in relation the one to the other as well as in relation to the primary winding, which is kept fixed.

A further object of the invention is to provide a high frequency current generator with a transformer, to the windings of which it is possible to give coupling values about 0 (in the case when all the turns of the secondary winding are folded up so as to present minimum areas), and about 1 (at least 0.85 in the case when all the turns of the secondary winding are unfolded, so as to present maximum areas), and also all the intermediate values, whereby the amount of energy transmitted by .said generator to the consuming apparatus can be continuously varied between its maximum value and an eventually very small fraction of said maximum value (for instance A still further object of the invention is to provide a high frequency current generator including a transformer in which the self impedance of the secondary winding is varied in same time and in same direction as its coupling with the primary winding, whereby the adjustment of the energy transmitted to the consuming apparatus brings about in same time the adaptation of the generator to its load, thereby making useless to determine accurately the induction coil for heating by induction.

A final object of the invention is to provide a high frequency current generator including a transformer, the two windings of which are connected in series with each other so as to highly increase the coupling of said windings and consequently the reactive energy transmitted to the consuming apparatus, whereby said consuming apparatus can be equipped for instance with an induction coil having a Q-factor equal to 40, whereas the known generators cannot feed induction coils having a Q-factor higher than from 8 to 15.

Several embodiments of a high frequency current generator according to the invention, specialy intended for the heating by induction, have been described below with reference to the annexed drawing, in which:

FIGURES l and 2 are respectively an elevation and a plan view of a first embodiment of the transformer with a continously variable coupling, with which the generator according to the invention is equipped.

FIGURE 3 is a circuit diagram of a Colpitts oscillator included in the generator according to the invention.

FIGURE 4 is a plan view of a second embodiment of the transformer with which the generator according to the invention is equipped. i

The transformer shown in FIGURES l, 2, of the drawing consists essentially of a fixed primary winding 1, formed in the considered example of several circular turns, and of a single turn 2, forming the secondary winding, also circular and arranged around the primary 1.

. The secondary turn 2 is made of three independent conductors: a semi-circular conductor 2 and two quadrantal conductors 2" and 2" of a slightly smaller radius. Each end of the semi-circular conductor 2 is connected by a hinge to one end of one of the quadrantal conductors 2", 2"; each hinge consists essentially of a pivotal axis, 3" or 3", integral with a part, 4 or 4" fixed at the end of the conductor 2" or 2", upon which engages, so as to turn with some friction, the part 5" or 5" fixed at one of the ends of the conductor 2'. At the ends of the conductors 2 or 2", remote from the parts 4 and 4", are fixed radial conductors 6", 6"; these conductors are insulated from each other and constitute the connections to the secondary turn 2.

Electrical continuity between the three conductors 2, 2", 2", forming the secondary turn is ensured by the parts 4", 4", 5", 5" and the hinge axes 3", 3" which connect them, said conductors being thereby joined in series.

The whole of the turn 2 is carried by an axial support 7 which forms the prolongation of the hinge axis 3", from which it is electrically insulated.

In the example shown, the half turn formed by the quadrantal conductors 2" and 2" remains fixed, as also the primary winding 1 with which it is concentric; on the other hand, the half-turn 2" can pivot about the hinge axes 3" and 3"; it becomes thereby possible to give to this half-turn 2 any inclined position intermediate between its horizontal position shown in full lines in the figures, and in which its area presented to the magnetic flux of the primary winding 1 is a maximum, and its horizontal position shown in dot-dash lines, in which the area presented by said turn 2 is practically zero; two of these intermediate inclined positions have also been shown in dot-dash lines. In the limiting horizontal position corresponding to the maximum effective area of the turn 2, the coupling of the windings 1 and 2 may reach the value 0.85 while it falls practically to zero in the other horizontal limiting position, and assumes, in a continuous fashion, every value between these two limits, as the half turn 2 is pivoted from one to the other of the two horizontal limiting positions. a

The oscillator shown in FIGURE 3 is of the classical type, known as a Colpitts oscillator, and it is essentially constituted by a three-electrode tube 8, the cathode of which receives its heater current through a transformer 9, said transformer being supplied through the choke coils 10, whereas its anode receives the necessary positive high voltage through the choke coil 11, and its grid is biased by a resistor 12 connected to the ground and shunted by a condenser 12': the inductance .part of the oscillating circuit is constituted by a transformer with a continuously variable coupling, such as illustrated in FIGURES 1 and 2; the primary 1 and the secondary 2 of said transformer are connected in series with each other; to the terminals of the variable inductance thus constituted are connected the capacitive divider 13-43 and the additional capacitor .14, which form the capacitance part of the oscillating circuit. The circuit is connected to the 7 anode of the tube 8 by a condenser a predetermined and constant fraction of the oscillating energy of said circuit, with a suitable amplitude and phase, is taken at the middle point of the divider 1313' and applied, so as to maintain the oscillations,'upon the'cathode' of tube 8 through the condensers 15, which are associated with the condensers 15' to keep the two windings of the heater transformer 8 at the same alternating voltage in relation to the earth. The induction coil 16, which is wound around the piece to be heated, is connected to the terminals of the secondary 2 of the autotransformer.

By pivoting the half-turn 2' between its two extreme positions (FIGURE 2), it is possible to vary the power delivered by the induction coil -16 in a continuous way between its maximum value and a very small fraction of said maximum value, for instance of it. on the other hand, the induction coil 16 can be fitted on the piece tobe'heated, irrespective of the value of the impedance of said coil, particularly without accurately adapting it to the oscillator; in fact, experiment and calculation have shown that this oscillator keeps on working in the best conditions even when the secondary 2 of its autotransformer supplies induction coils having very different impedances, for example in the ratio of 1 to 20. Moreover, the autotransformer allows to supply the induction coil with a sufficient amount of reactive energy, even if said coil presents a Q-factor as high as 40.

The autotransformer shown'in FIGURE 4 differs only from the autotransformer of FIGURES 1 and 2 in that its secondary 2 includes two circular turns, each diametrally divided in two half-turns: a fixed half-turn 2" 2' 2" 2" provided with the connections 6" and 6' of the winding, and the other 2 -2 pivoting round insulated axes 3"and 3'; a brazing 17 establishes an electric connection between one of the ends of the primary 1 and the end 6" of the secondary 2. 7

Within the scope of the present invention are also embodiments of the auto-transformer which differ parful for the making of transformers with two symmetrical half-secondaries.

(2) The secondary winding is inside the primary windmg.

(3) The turns of the primary and secondary windings can have any desired form, not circular, for example rectangular or square.

The characteristics of these variedembodiments can also be combined together within the scope of the present invention.

What I claim is: e

1. A device for generating a high frequency heating energy in a load, including an electric oscillator and means to transfer a continuously variable part of the oscillating energy from said oscillator to the load, said means comprising a fixed air-core coil connected with said oscillator and curved conductors, disposed coaxially with said fixed coil and hinged to each other, so as to be electrically connected in series and to be pivot-ally displaceable in relation to each other and to the fixed coil,

said conductors being coupled with the load.

2. The device of claim 1, in which two of the curved said oscillator, a number of fixed curved conductors disposed coaxially with each other and wit-h'the fixed coil,

engagingwith their erspective ends said insulated axes between the ends of said fixed conductors, so as to be together pivotally'displaceable in relation to said fixed conductors and air-core coil, and means to electrically connect the ends of each fixed conductor with the adjoining ends of one of the displaceable conductors, so as to form a plurality of coaxial turns connected in series with each other.

4. The device of claim 3, in which each fixed conductor is longer than the displaceable conductor with which it is connected'so as to form a turn.

5. The device of claim 3, in which the structure formed by'the fixed and displaceable conductors hinged to each other is supported by at least one of the insulated axes, and means are provided .to drive together the displaceable conductors through one of said insulated axes.

6. The device of claim 3, in which the fixed and displaceable conductors are half-circular, the two insulated axes being aligned with each other.

7. A high frequency current generator for high fretwo parts, hinged the one to the other, so as to be pivotally displaceable in relation the oneto the other and to the fixed primary winding, and means to transfer the oscillatingenergyfrom said transformer secondary winding to the piece to be heated.

8. A high frequency current generator for induction heating, including a high frequency autotransf-ormer, the secondary winding of which has at least one of its turns made in two parts, hinged the one to the other, so as to be pivotally displaceable in relation the one to the other and to the fixed primary winding; capacitors co n c ed.

across said autotransformer so as to form a one-tapped voltage divider, a multi-electrode electron tube with suitable heating, supplying and biasing means, a capacitive connection between one terminal of said autotransformer and the output electrode of said electron tube, a connection between the tap of said voltage divider and the control electrode of said electron tube, and an induction coil connected across the secondary winding of said autotransformer.

References (Zited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Germany May 16, 1957 

